This invention relates to a veneer lathe (peeling machine) provided with a roller bar for peeling a monolithic veneer (hereinafter referred simply to as a veneer) from a log.
There is known a veneer lathe provided with a roller bar, which is designed to peel (or cut off) a veneer from a log by making use of a knife as disclosed in U.S. Pat. No. 3,670,790 (Porter et al. issued on Jun. 20, 1972) wherein the roller bar is arranged parallel with the cutting edge of the knife for cutting a log and is held rotatably in a recessed portion of a holder. More specifically, the recessed portion of the holder is circular in cross-section having a diameter substantially corresponding to the outer diameter of the roller bar, and the roller bar is rotatably sustained (i.e. it is driven following the rotation of the log) in the recessed portion.
There is also known another type of veneer lathe provided with a nose bar-roll having a relatively large diameter as disclosed in U.S. Pat. No. 4,602,663 (Browning, Jr. et al. issued on Jul. 29, 1986) wherein the nose bar-roll is arranged parallel with the cutting edge of the knife for cutting a log and is held rotatably in a recessed portion of a holder. More specifically, the recessed portion of the holder is circular in cross-section having a diameter substantially corresponding to the outer diameter of the roller bar, and the nose bar-roll is rotatably sustained (i.e. it is designed to be driven by driving means) in the recessed portion.
In the case of the former veneer lathe (Porter et al), since the roller bar may be relatively small in diameter, the roller bar for pressing a log can be positioned immediately before the log is cut by the knife, so that the roller bar can be sufficiently functioned as a pressure bar, thus making it possible to obtain a veneer which is relatively smooth in surface and relatively free from so-called lathe check. However, since the force for rotating the log cannot be transmitted from the roller bar, a chuck is employed to press the axial portion of the log so as to transmit any required force from the chuck to the log for cutting the log. Therefore, once the axial portion of the log becomes fragile, the log is broken due to the power transmitting force of the chuck, thereby making it impossible to further continue the peeling work of the veneer lathe.
On the other hand, in the case of the latter veneer lathe (Browning Jr. et al), the driving power required for cutting can be supplied from the nose bar-roll, so that even a log which becomes fragile at the axial portion thereof can be allowed to be peeled. However, since the diameter of the nose bar-roll is relatively large in diameter (at least 15 times as large as the thickness of veneer to be cut by the lathe), if the nose bar-roll is positioned immediately before the knife thereby to sufficiently press a log in order to prevent the lathe check, an excessive force is acted on the log as a whole, so that the log is often caused to bend whereby making it impossible to obtain a veneer of uniform thickness. Therefore, the veneer lathe of this type cannot be positioned immediately before the knife so that a log cannot be sufficiently pressed at the position immediately before the knife. As a result, the nose bar-roll cannot be sufficiently functioned as a pressure bar. Because of this, it is difficult with the veneer lathe of this type to prevent the generation of so-called "fore-splitting", i.e. a splitting that is to be generated immediately before the cutting edge of knife at the occasion of peeling a log. Additionally, the surface of veneer to be obtained would be markedly roughened and at the same time, a big lathe check tends to be generated in the veneer.